1. Field of The Invention
The present invention relates to a method for processing hot briquetted direct reduced iron (DRI) during a cooling and screening step of the briquetting process.
2. Description of Related Art
Direct reduced iron is produced by heating iron ore in a hot reducing gas atmosphere so as to strip oxygen from the ore to obtain iron-rich xe2x80x9csponge-ironxe2x80x9d. The sponge iron which maintains substantially the same shape as the iron ore processed, is relatively fragile and has a tendency to revert to the oxide state during storage. To facilitate handling, shipping and storage the sponge iron is formed into dense, often pillow shaped, briquettes referred to as xe2x80x9cHBIxe2x80x9d (hot briquetted iron).
The briquettes are most commonly formed by introducing the sponge iron, while still hot from the reducing gas processing step, between closely spaced cylindrical rolls having a series of opposed pockets in the cylindrical surfaces into which the sponge iron enters and is compacted to form the briquettes. The briquettes exit the rolls with a thin land between them resulting from a small spacing between the rolls. Following exit from the rolls, a breaker separates the connected briquettes. Such breaking step results in fragments of the briquettes being present which must be separated from the formed briquettes in a screening operation.
U.S. Pat. No. 4,236,699 describes a number of processes for treatment of the briquettes following exit from the briquetting press. In a process depicted in FIG. 3 briquettes along with fragments and fines are first cooled in a rotary cooler utilizing an inert gas and water. Following cooling of the briquettes, fragments and fines are screened to separate the various components. In processes depicted in other figures, the briquetting process receives already cooled metallized powder for forming briquettes.
U.S. Pat. No. 5,630,202 describes processes depicted in FIGS. 1 and 2 wherein, following briquetting between cylindrical rolls and separation of the resulting connected briquettes, the briquettes, fragments and fines are screened while still hot. The hot fragments and fines are recycled to the cylindrical rolls for compaction while the briquettes are conveyed to a cooling devise for cooling.
East Germany Patent No. 20,740 shows, in FIG. 3, screening lump shaped material in a still hot condition, then cooling oversized material in a water tank while conveying undersized material while still in the hot condition.
It is the object of the present invention to provide a method and apparatus to overcome problems associated with prior practice screening of hot briquetted iron.
The present invention provides a means to avoid the problems associated with conveying and screening hot briquetted iron while still at an elevated temperature. Hot screening and conveying of hot fines and briquettes while at a briquetting temperature between about 600 to 700xc2x0 C. present severe demands on processing equipment. The present invention quenches the briquettes in an early step of the process so as to eliminate exposure of screening and conveying equipment to such harsh high-temperature processing conditions.
Both quenching and screening are carried out concurrently in a single operation wherein a robust coarse screen submersed in a water bath cools and separates the briquettes from the fragments. The briquettes, which form the larger portion of the material being processed and constitutes most of the weight, is conveyed across the screen and out of the bath to storage or shipment with little additional handling. Fragments, which pass through the screen, and which are a minor portion of the material being processed, can be further screened, to obtain an assortment of sizes for various markets, with use of less rugged screening equipment requiring less capital expenditure and reduced maintenance.
Specific features and contributions of the invention are described in more detail with reference being made to the accompanying drawing.